The objective of this effort is to develop and market a mailable thermoluminescent dosimeter (TLD) device and readout service suitable for frequent, periodic monitoring of radiation beam calibrations at medical institutions treating cancer patients with cobalt-60 units and electrical linear accelerators, and having inadequate physics support. The specific aims are: 1) To utilize current scientific knowledge and the ten-year experience of the NCI-funded Centers for Radiological Physics in the use of mailed TLDs to develop design criteria for a prototype system; i.e., a positioning jig/miniphantom with self-contained TLD inserts. 2) To remedy those aspects of currently used TLDs which hinder commercial application; specifically, labor-intensive individual assembly and readout, and difficulty in proper beam placement when used by personnel other than trained medical physicists. 3) To construct and field-test prototypes at eight cancer treatment facilities chosen for the variety of machines in use, geographical location, availability of qualified consultants who normally perform the calibrations, and the facility's potential as a commercial user. 4) To analyze data from 160 TLD samples irradiated in 15 beams for a) accuracy as determined by standard chamber calibrations, and b) positioning device convenience and freedom from error. At the end of Phase I, it is expected to have demonstrated a prototype device and service which can be profitably marketed to cancer treatment facilities desiring to cost-effectively monitor their radiation beams with the frequency required for quality patient care. Also, to have accumulated sufficient cost statistics and manpower requirements to form the basis for pricing and organizational structure development in Phase II.